History doesn’t get better than this. Nicolaevsky was one of the great socialist historians, author of a terrific biography of Karl Marx, and participant in the 1917 revolution in Russia.

In this book, written some years after he was deported from the USSR, he reveals the true story of the most successful “mole” ever planted by the tsarist police in the ranks of the Russian revolutionary movement. Ievno Azef (the preferred spelling today) rose in the ranks of the Socialist Revolutionary Party in the years leading up to the first world war, eventually becoming the head of its feared “Combat Organisation”. In that role, he both betrayed revolutionaries to the police while at the same time carrying out successful acts of terror, including the murder of members of the extended royal family.

Nicolaevsky describes Azef’s double life in breathless prose, and his telling of the story compares favourably with anything John LeCarrè or Graham Greene ever wrote.

Upon his exposure by the “revolutionary bloodhound” Vladimir Burtsev, leaders of his party continued to insist on Azef’s innocence. This was a pattern of behaviour also displayed by the Bolsheviks, when Lenin defended their own Okhrana “mole” Roman Malinovsky, head of their Duma faction, certain of his innocence. (Malinovsky, unlike Azef, eventually faced revolutionary justice.) Decades later, Trotsky’s insistence that Stalin could not have been a tsarist police spy echoed these earlier views.